Dr. Igor J. Korainik received his medical degree from Geneva Medical School, Switzerland. He subsequently performed a residency in Internal Medicine at the Geneva University Hospital. He then received post-doctoral training in Molecular Virology in Dr. R.C. Gallo's laboratory at the National institutes of Health. he is currently in his last year of residency in Neurology at the Harvard-Longwood Neurology Training Program. He will be made Instructor in Neurology at Harvard Medical School's Beth Israel hospital immediately after his residency. He plans a full-time career as an academic investigator and teacher. The support he would receive from this award would play an important part in his growth to scientific independence. JC virus (JCV) is the etiologic agent of Progressive Multifocal Leukoencephalopathy (PML). The determinants of JCV quiescence and spread in the body as well as the exact cell type carrying JCV in the blood remain unknown. The nature of the immune response which prevents the onset of PML in the immunocompetent population and most HIV-infected individuals has not been elucidated. Dr. Koralnik will determine the prevalence and the genetic variation of JCV in the blood and cerebrospinal fluid of patients with HIV infection, and he will identify the phenotype of JCV-infected cells. He will also characterize the cellular immune response to JCV. Finally, he will attempt to establish a non-human primate model of Pml. Dr. Koralnik's scientific growth will be achieved in the Division of Viral Pathogenesis (Dr. Letvin, Chief) and the Neurology Department at the Beth Israel Hospital (Dr. Saper, Chairman). The technical expertise and commitment to work in elucidating the immunopathogenesis of PML in the setting of AIDS by other members of the Division of Viral Pathogenesis and the Neurology Department will immeasurably assist Dr. Koralnik in his scientific progress. Dr. Letvin and Dr. Saper are fully committed to Dr. Koralnik's development as an independent investigator.